I would say Cryo is the best place to mine because it has the endgame ores (galvanium, titanium, antanium) while not being full of lava or bomber skeletons. It's also pretty easy to get around in as the raw ice is fast to break. For gems I found lillith to have more tourmaline and tanzanite, Magmar there are more rubies, Xeno there are more emeralds, alba seems to have more diamonds and Seth seems to have more citrine.